Harry comes to understand that "writing equals life and not writing equals death" (Marc Seals). The time to write was over and now all the things he had held back (because he feared he did not know enough, or had other plans, or whatever interrupted the writing process) would never be written. Here is this realization at the end of the story, as Harry lays minutes from death:

No, he thought, when everything you do, you do too long, and do too late, you can't expect to find the people still there. The people all are gone. The party's over and you are with your hostess now.

Death is the hostess, of course. A rather grim party.